Electrically heated transparent panel and prtective circuit therefor



Apr-11 23, 1968 J. G. MARRIOTT ELECTRICALLY HEATED TRANSPARENT PANEL AND PROTECTIVE CIRCUIT THEREFOR 2 Sheets-Sheet 1 Filed May 26. 1966 all m 4 INVENTOR. gmaLzfifija/acedt BY 716% f Jcw A TTOR NEYX April 23, 1968 .1. G. MARRIOTT 3,

ELECTRICALLY HEATED TRANSPARENT PANEL AND PROTECTIVE CIRCUIT THEREF OR Filed May 26, 1966 2 Sheets-$heet INVENTOR.

j 7 game/1.15. film/ma 2 0566% temps ATTORNEYS United States Patent 3,379,859 ELECTRICALLY HEATED TRANSPARENT PANEL AND PROTECTIVE CIRCUIT THEREFOR James G. Marriott, Perrysburg, Ohio, assignor to Libbey- Owens-Ford Glass Company, Toledo, Ohio, 2 corporation of Ohio Filed May 26, 1966, Ser. No. 553,171 14 Claims. (Cl. 219-522) The present invention relates generally to an electrical circuit protector, and more particularly to a device for interrupting the flow of current to an electrically heated glass panel upon breakage of the panel.

Refrigerated cabinets are commonly used to store, and at the same time display, goods which are perishable or must otherwise be maintained at lower than room temperature in retail outlets such as supermarkets and carryouts. Generally, display cabinets of this type are characterized by a storage compartment defined by insulated walls and maintained at a relatively cool temperature by suitable refrigeration mechanism. Access to the cabinet is afforded by one or more doors movable between open and closed positions. Glazed areas or windows are commonly employed in the doors to permit shoppers to view the goods within the cabinet without opening the doors and exposing the compartment to the ambient atmosphere.

The efficiency, and resulting cost of operation, of refrigerated units of this type is, of course, dependent to a large extent upon how well the refrigerated compartment is insulated from the relatively warmer atmosphere of the room in which the cabinet is located. The cabinet generally has double walls which can be insulated as necessary to restrict heat transfer therethrough, so that there is proportionately more heat transfer through the glazed areas or windows. In order to retard this heat transfer through the windows, they may be glazed with socalled multiple sheet or insulating glazing units.

Various types of such units are well known in the art, and generally comprise spaced sheets of glass sealed together around their marginal or peripheral edges to form an enclosed air space or chamber therebetween, which space may be filled with dehydrated air or may be exhausted to provide a partial vacuum. The dead air space between the glass sheets of the unit constitutes an insulating medium retarding the transfer of heat through the window.

It will be readily appreciated that when employed in refrigerated cabinets, one side of a window, hereinafter referred to as the compartment side, is exposed to the cool atmosphere of the refrigerated compartment while the other side, hereinafter referred to as the room side, is exposed to the ambient atmosphere surrounding the unit, which is ordinarily relatively warm as compared to the interior of the cabinet. Due to the transfer of heat through the window, the room side surface is maintained at a temperature which is below room temperature. If this surface is cooled to a temperature below the dew point temperature of the surrounding atmosphere, the moisture present in the room atmosphere will condense on the surface. This condensation is not only unsightly and messy but also, if it occurs in sutficient quantity, may interfere with or completely obstruct vision through the window, thereby frustrating its intended purpose.

Under adverse conditions, when the dew point temperature of the atmosphere is comparatively high, the insulating qualities of multiple sheet glazing units may not be sufficient to prevent the temperature of the room side of the unit from being lowered below the dew point. More-over, even if the temperature of the room side surface is not lowered sufficiently to cause condensation thereon, it will be apparent that when the door is opened and exposed to the room atmosphere, moisture quite 3,379,859 Patented Apr. 23, 1968 readily condenses on the inner surface or compartment side surface of the window, since this surface is maintained at a relatively low temperature by being exposed to the refrigerated compartment. When the door is then closed, the condensate on the cabinet side surface is exposed to the frigid atmosphere of the compartment so that it is not readily dissipated but rather tends to freeze and produce an opaque frost.

In order to retard the condensation of moisture on the surface of the glass sheets and to rapidly dissipate this condensation and prevent it from freezing should it form, heating means may be positioned within the air space of the glazing unit. The sheets are then heated sufficiently so as to retard the condensation of moisture and promote the evaporation of condensation which might occur under severe conditions.

A transparent electrically conductive film or coating placed on the inner surface of at least one of the sheets of the glazing unit has been found very effective and efficient as the aforementioned heating means. Since the film is adhered direct-1y to the inner surface of the sheet and is in an inaccessible location, it is protected from damage due to marring or scratching, which damage might impair operation of the film. In addition, the sheets act as an insulator to insure that the electricity will not be conducted outwardly of the unit.

The electrically conducting film must, of course, be connected to a source of electrical energy. The doors in which the glazing units are often mounted must be capable of being opened and closed as, for example, by a sliding or swinging action in the customary manner. Thus, it is necessary that the connection between the electrically conducting film and the source of electrical energy provide for this relative movement between the door and the cabinet. Since the doors are subjected to repeated opening and closing, there is ever present the possibility that a malfunction may occur in the linkage connecting the film and power source, resulting in the possibility of persons coming in contact with the unit being subjected to an electrical shock. Likewise, either or both of the glass sheets of the unit might accidentally be broken, whereby persons may come in contact with the electrical system thereof.

It is an object of the present invention to provide an electrically heated multiple sheet glazing unit for use in refrigerated cabinets as described above which avoids the possibility of users of the cabinet being subjected to an electrical shock.

Another object of the invention is to provide an electrically heated multiple sheet glazing unit in which the supply of electrical current to the unit will be automatically discontinued in the event of an interruption in the current due to a break in the electrical circuit.

Still another object of the invention is to provide an electrically heated multiple sheet glazing unit in which the supply of electrical current will be automatically discontinued in the event of breakage of either of the glass sheets forming the unit.

Yet another object of the invention is to provide an electrically heated multiple sheet glazing unit of the above character which is relatively simple, inexpensive to construct and maintain, and positive in operation.

Other objects and advantages of the invention will become more apparent during the course of the following description when taken in connection with the accompanying drawings.

In the drawings, wherein like numerals are employed to designate like parts throughout the same:

FIG. 1 is a perspective view of a door for a refrigerated cabinet in which is mounted a glazing unit constructed in accordance with the invention;

FIG. 2 is a perspective view of the glazing unit itself, and showing the circuitry through which the device is connected to a source of electrical energy;

FIG. 3 is a sectional view through the unit taken substantially along line 3--3 of FIG. 2;

FIG. 4 is a fragmentary sectional view taken substantially along line 4-4 of FIG. 2;

FIGS. 5 and 6 illustrate, in plan view, the inner surfaces of the two sheets of the novel glazing unit, the lower edge of the sheet in FIG. 5 being adapted to mate with the upper edge of the sheet in FIG. 6; and

FIG. 7 is a sectional view taken substantially along line 7--7 of FIG. 4.

While the present invention is not limited to the use of any particular construction of refrigerated cabinet or to any particular type of multiple sheet glazing unit, it has been shown solely for purposes of illustration herein in connection with a so-called glass-metal type unit, wherein the glass sheets are secured in spaced relation by a metallic separator strip. The invention could be applied to other types of units, such as the well-known all-glass and mastic-type units as well. In the all-glass unit the marginal edge portions of the glass sheets are heated to a temperature at which they become pliable and are thereafter urged toward and into fusion contact with one another to form a sealed edge wall extending around the unit. In the mastic-type unit, the sheets are maintained in spaced face-to-face relationship by a separator strip of plastic or a similar material cemented thereto by an adhesive material.

Turning now to FIG. 1 of the drawings, there is shown generally at 11 a door for a refrigerated cabinet constructed in accordance with the invention and including a frame 12 in which is mounted a multiple sheet glazing unit 13. A handle 14 is atatched to the frame to assist in opening the closing the door, which may be mounted on the cabinet in any conventional fashion as by hinges so that it swings open and closed, or in a track so that Opening and closing is accomplished by sliding the door along the track. While the glazing unit is referred to herein as being mounted in a door, it will readily be appreciated that it could as well be mounted as a fixed window in a refrigerated cabinet.

The glazing unit 13, as best illustrated in FIGS. 2, 3 and 7, includes sheets of glass 15 and 16 secured together in spaced relation by a relatively thin metallic separator strip 17 extending around the marginal edges of the unit to form an air space 18 therebetween, which space may be filled with dehydrated air or gases or exhausted to provide a partial vacuum. The separator strip is hermetically sealed to the glass sheets through the medium of solder fillets 19 joining the separator strip to metallic coatings 20 adherent to the marginal edge portions of the glass sheets.

A transparent electrically conductive film or coating 21 is adhered to the inner surface of the sheet 15 within the air space 18 so that when an electric current is supplied to the film as will be hereinafter explained, the film will be heated and will, in turn, heat the glass sheets 15 and 16. The invention is not limited to any particular electrically conductive film, but rather contemplates that any film which meets the requirements regarding transparency and electrical conductivity may be utilized within the spirit of the invention. By way of example, very good results may be obtained with a tin oxide film of the type described in Patent No. 2,429,420, dated Oct. 21, 1947.

In order to supply electrical power to the film 21 on the sheet, metallic electrodes 22 are afiixed to the sheet in contact with the film along opposite edges thereof. When connected to a source of electrical energy, the current then flows between the electrodes through the film, causing it to be heated. In order to insure that the film is electrically insulated from the separator strip 17 and to facilitate fabrication of the glazing unit, the film terminates inwardly of the outer edges of the glass sheets. Thus, as best illustrated in FIGS. 3, 4, 6 and 7, both the edges of the film and the electrodes 22 are spaced inwardly from the metallic coating 2 to which the separator strip is secured, thereby isolating the film and electrodes from the separator strip.

The unit could be made operational, of course, by merely connecting the opposite electrodes 22 to a source of electrical energy. However as explained above, should the unit then be broken or if some other malfunction should occur, current would continue to be supplied and persons using the refrigerated cabinet would be subjected to an electrical shock hazard. According to the invention, this shock hazard is eliminated by providing a built-in circuit protector which causes the power supply to the unit to be discontinued in the event of any interruption or discontinuity of any type, even momentarily, in the power supply circuit. Thus, if either of the glass sheets and electrodes or conductive strips thereon should be cracked or broken, or if the flexible wire or other means connecting the unit to the power supply should break, the unit will immediately be disconnected from the power supply. As illustrated in FIG. 2, this is accomplished by causing both sheets of the unit to form an integral portion of the circuit by which power is supplied to the film 21, and placing in the circuit a solenoid-operated relay which is held closed by the passage of current through the circuit.

In order to provide an external electrical connection for the electrodes 22, conductors 23 such as ordinary wires are afiixed thereto as by soldering, and the conductors are connected to prongs 24 extending through and sealed in pass-through insulators 25 within the separator strip 17. Conductive strips 26 are formed on the nonheated glass sheet 16 to provide a path along the sheet for the electric current so that if this sheet is broken, a discontinuity will be created in the electrical circuit. The conductive strips can be formed of any suitable conductive material which will adhere to the glass and which will break and form a discontinuity when the sheet itself is broken. Thus, the strips might be deposited as a metallic solder or might be fabricated from a conductive bakeon paint. In order to insure that the conductive strips will be broken by any break in the glass sheet 16, it is preferred that they extend along the edges of the unit 13 substantially coextensive with the electrodes 22, and additionally extend along a third edge of the unit toward the center as shown in FIGS. 2 and 5. As will be hereinafter apparent, the strips could be placed at other locations on the sheet so long as they did not objectionably obstruct the viewing area.

Spring contacts 27 soldered or otherwise secured to the electrodes 22 at the ends opposite the conductors 23 engage the conductive strips 26 on the sheet .16 and create a path for the flow of electric current from the electrodes to the conductive strips. Additional spring contacts 28, carried by prongs 29 sealed in and insulated from the separator strip 17 by pass-through insulators 30, engage the conductive strips at their opposite ends and provide an external electrical connection thereto. The spring contacts 28 are insulated from the electrically conducting film 15 in a suitable manner as by a strip of insulating material 31 inserted between the contacts and the film.

One suitable system for connecting the glazing unit 13 to a supply of electrical power in accordance with the invention is illustrated in FIG. 2. As shown therein, a line 32 from one side of a conventional volt 60 cycle power source (not shown) is connected to one of the prongs 24 leading to an electrode 22 at one edge of the film 21. A second line 33 extends from the other side 34 of the power source to one set of contacts 35 of a solenoid-actuated double-pole relay 36. A line 37 connects the contacts 35 to the prong 24 joined to the other of the electrodes 22, thereby forming a circuit through the electrodes 22 and film 15.

A second circuit extends through a line 38 from one of the prongs 29 to the solenoid 39 of the relay 36, a line 40 from the solenoid to the other contact 41 of the relay 36, and a line 42, to the other of the prongs 29. The contacts 35 and 41 of the relay 36 are biased to 'a normally open position by a spring 43.

For purposes of energizing the solenoid 39 to close the contacts as will be hereinafter explained, a line 44 extends from the power source 34 through a manual reset switch 45 to the line 40 which, in turn, is connected through the solenoid and line 38 to the pron-g 29 and thus to the other side 32 of the power source. The reset switch is biased to a normally open position by a spring 46.

To initiate operation of the unit, the reset switch 45 is momentarily depressed, completing a circuit from line 34 through line 40, solenoid 39, line 38, prong 29, spring contact 28, conductive strip 26, spring contact 27, electrode 22 and prong 24 to line 32, and thereby energizing the solenoid to close the contacts 35 and 41. Closing the contact 35 completes a circuit from line 34 through line 33, line 37, prong 24, electrode 22, film 15, the other electrode 22, and prong 24 to the line 32, so that the unit v13 is heated. Simultaneously, closing of the contact 41 completes 'a circuit from one of the electrodes 22 through spring contact 27, conductive strip 26, spring contact 28, prong 29, line 38, solenoid 39, line 40, contact 41, line 42, prong 29, spring contact 28, conductive strip 26, and spring contact 27 to the other of the electrodes 22. The solenoid thus remains energized when the manual reset switch 45 is released.

In the event that the sheet 15 and one of the electrodes 22 thereon are accidentally broken, the current through the above circuit will be interrupted so that the solenoid will be de-energized and the relay 36 will be opened by the spring 43. As the contact 35 opens, the unit is disconnected from the power source 34 and the shock hazard is immediately removed. Likewise, if the sheet 16 and conductive strips 26 thereon should be broken, the circuit will be interrupted to de-energize the solenoid and open the relay. Any break in the wiring or in the connections to the unit that results in even a momentary interruption of power will cause the relay to be opened and the unit to be disconnected from the power source.

Of course, the relay will also be caused to open by momentary failure of the power supply. In order to reactivate the heating system of the glazing unit when power is restored in such instances, it is only necessary to momentarily depress the manual reset switch. It is contemplated that a signal light might be installed in conventional fashion so as to be illuminated when the relay is open and thereby alert store personnel to the fact that the heating system is not operating.

It is to be understood that the form of the invention herewith shown and described is to be taken as a preferred embodiment of the same, and that various changes in the shape, size and arrangement of parts may be resorted to 'without departing from the spirit of the invention.

I claim:

1. In a connection for conducting electrical energy from a source of said energy to an electrically conductive coating on a surface of a non-conductive panel, first means connecting one edge of said coating to one side of said source of electrical energy, second means connecting an opposite edge of said coating through a first relay to the other side of said source, and a protective circuit connected between said edges of said coating, said protective circuit containing means operable to open said relay in response to any interruption of current flow through said first and second connecting means and coating to thereby disconnect said panel from said source of electrical energy.

2. A connection for conducting electrical energy from a source of said energy to an electrically conductive coating on a surface of a non-conductive panel as claimed in claim 1, wherein said means operable to open said relay comprises a solenoid maintaining said relay closed while said solenoid is enengized, and means biasing said relay to a normally open position when said solenoid is de-energized.

3. A connection for conducting electrical energy from a source of said energy to an electrically conductive coating on a surface of a non-conductive panel as claimed in claim 2, said first and second means connecting opposite edges of said coating to said source of electrical energy comprising electrodes adherent to the surface of said panel along said opposite edges of said coating and electrically connected thereto, and said solenoid being electrically connected to said electrodes.

4. A connection for conducting electrical energy from a source of said energy to an electrically conductive coating on a surface of a non-conductive panel as claimed in claim 2, including a second relay in said protective circuit adapted to open simultaneously with said first relay and break said protective circuit through said solenoid.

5. A connection for conducting electrical energy from a source of said energy to an electrically conductive coating on a surface of a non-conductive panel as claimed in claim 4, including conductor means bypassing said second relay and electrically connecting said solenoid to said other side of said source of electrical energy, and a reset switch in said conductor means, said reset switch being normally biased in open position and adapted for momentary manual closure to energize said solenoid and thereby close said first and second relays.

6. An electrically heated multiple sheet glazing unit, comprising a pair of glass sheets joined around their marginal edges in spaced relation to form an enclosed airspace therebetween, an electrically conductive coating adhered to the interior surface of one of said sheets within said airspace, first conductor means connecting one edge of said coating to one side of a source of electrical energy, second conductor means connecting the opposite edge of said coating to the other side of said source of energy for passing an electric current through said coating, a relay in one of said conductor means, and a protective circuit electrically connected between the opposite edges of said coating, said protective circuit including means operable to open said relay in response to interruption of current flow through said first and second conductor means and said coating and to thereby disconnect said glazing unit from said source of electrical energy.

7. An electrically heated multiple sheet glazing unit as claimedvin claim 6, wherein said means operable to open said relay includes means biasing said relay to a normally open position and a solenoid in said protective circuit adapted to maintain said relay closed when said solenoid is energized and permit said relay to open when de-energized.

8. An electrically heated multiple sheet glazing unit as claimed in claim 7, including a relay in said protec tive circuit operable to open and close simultaneously with said relay in said conductor means so as to disconnect said protective circuit from said power source upon de-energizing of said solenoid.

9. An electrically heated multiple sheet glazing unit as claimed in claim 8, wherein said solenoid is electrically connected through said glazing unit to one side of said source of electrical energy, including a line bypassing said relay in said protective circuit and electrically connecting said solenoid to the other side of said source, and a reset switch in said line, said reset switch being normally biased open and adapted for momentary closure to energize said solenoid and thereby close said relays in said conductor means and said protective circuit.

10. An electrically heated multiple sheet glazing unit as claimed in claim 6, said first and second conductor means including a pair of electrodes adhered to said interior surface of said one sheet along opposite edges of the coating and electrically connected to said coating.

11. An electrically heated multiple sheet glazing unit as claimed in claim 10, including a pair of conductive strips adhered to the interior surface of the other of said glass sheets, one of said conductive strips being electrically connected to each said electrode, and said protective circuit being electrically connected to said conductive strips.

12. An eletrically heated multiple sheet glazing unit as claimed in claim 11, wherein each said conductive strip extends along the marginal edge of said other sheet opposite a corresponding one of said electrodes and substantially coextensive therewith, and along a third marginal edge toward the middle of said sheet, the ends of said conductive strips along the third marginal edge being adjacent to and spaced from one another.

13. An electrically heated multiple sheet glazing unit as claimed in claim 12, wherein the glass sheets are joined in said spaced relation by a metallic separator strip secured to the interior surface of said sheets around the marginal edges thereof, said electrodes, conductive strips and electrically conductive coating being spaced inwardly from said separator strip, comprising an electrical contact secured to each said electrode at one end thereof and engaging the corresponding conductive strip on said other sheet, said first and second conductor means including means connected to the other end of each said electrode and extending through and insulated from said 35 metallic separator strip for connecting said electrodes to said source of electrical energy, and additional electrical contacts engaging said adjacent ends of said conductive strips and having means extending through and insulated from said metallic separator strip for connecting said additional contacts to said protective circuit, said additional contacts being insulated from said electrically conductive coating.

14. An electrically heated multiple sheet glazing unit as claimed in claim 12, said means operable to open said relay in said conductor means including means biasing said relay to a normally open position, a solenoid in said protective circuit adapted to maintain said relay closed while said solenoid is energized and permit said relay to open when de-energized, a relay in said protective circuit operable to open and close simultaneously with said relay in said conductor means so as to disconnect said protective circuit from said source of electrical energy upon de-energizlng of said solenoid, a line bypassing said relay in said protective circuit and connecting said solenoid to the other side of said source, and a reset switch in said line, said reset switch being normally biased open and adapted for momentary manual closure to energize said solenoid and thereby close said relays in said conductor means and said protective circuit.

References Cited UNITED STATES PATENTS 2,557,905 6/1951 Burton et al. 219-213 2,625,640 1/1953 Gaiser et al. 219-522 2,787,696 4/1957 Karp et al. 219-203 2,806,118 9/1957 Peterson 219-203 2,927,441 3/1960 Sharpe et al. 219-248 RICHARD M. WOOD, Primary Examiner.

VOLODYMYR Y. MAYEWSKY, Examiner. 

1. IN A CONNECTION FOR CONDUCTING ELECTRICAL ENERGY FROM A SOURCE OF SAID ENERGY TO AN ELECTRICALLY CONDUCTIVE COATING ON A SURFACE OF A NON-CONDUCTIVE PANEL, FIRST MEANS CONNECTING ONE EDGE OF SAID COATING TO ONE SIDE OF SAID SOURCE OF ELECTRICAL ENERGY SECOND MEANS CONNECTING AN OPPOSITE EDGE OF SAID COATING THROUGH A FIRST RELAY TO THE OTHER SIDE OF SAID SOURCE, AND A PROTECTIVE CIRCUIT CONNECTED BETWEEN SAID EDGES OF SAID COATING, SAID PROTECTIVE CIRCUIT CONTAINING MEANS OPERABLE TO OPEN SAID RELAY IN RESPONSE TO ANY INTERRUPTION OF CURRENT FLOW 